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TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Physics > Ultraviolet Light

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Wavelength: 10m to 3.5 × 10m

Sources

Ultra hot bodies, mercury vapor lamp, electric arcs (sparks).

The mercury vapor lamp works by photoelectric effect (exciting e- in the mercury and thus releasing photons of the right frequency).

Detection

Photographic plates, fluorescence of certain chemicals, photocells, photoelectric devices.

Uses

UV light produces vitamins (in particular Vitamin D) in the skin and causes sun-tans. Note, though, that UV light is harmful even in modestly large doses. The shorter the wavelength the more dangerous the UV light is. It is used in bacteriology to kill some cells.

Notes

UV light was found shortly after infrared (early 1800s). Much of the UV light emitted by the sun is absorbed by the ozone layer in the Earth's atmosphere. Since our eyes are especially sensitive to UV light, a UV lamp should never be viewed directly. Snow-blindness, which is what skiers suffer from when skiing on sunny areas, is caused by UV. Manufacturers of washing powders often add fluorescent powders to their products to live up to the claim that their product washes whiter than white, since these powders will absorb UV light and re-radiate it as bright visible light.

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